6.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2025-68113

CVE-2025-68113: ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay

Impact

A cryptographic semantic binding flaw in ALTCHA libraries allows challenge payload splicing, which may enable replay attacks. The HMAC signature does not unambiguously bind challenge parameters to the nonce, allowing an attacker to reinterpret a valid proof-of-work submission with a modified expiration value. This may allow previously solved challenges to be reused beyond their intended lifetime, depending on server-side replay handling and deployment assumptions.

The vulnerability primarily impacts abuse-prevention mechanisms such as rate limiting and bot mitigation. It does not directly affect data confidentiality or integrity.

Patches

This issue has been addressed by enforcing explicit semantic separation between challenge parameters and the nonce during HMAC computation.

Users are advised to upgrade to patched versions.

Workarounds

As a mitigation, implementations may append a delimiter to the end of the salt value prior to HMAC computation (for example, <salt>?expires=<time>&). This prevents ambiguity between parameters and the nonce and is backward-compatible with existing implementations, as the delimiter is treated as a standard URL parameter separator.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2025-68113

CVE-2025-68113:

6.5

CVSS Score

3.1

-

CVSS Score

Basic Information

Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
altcha-lib	npm	< 1.4.1	1.4.1
altcha-org/altcha	composer	< 1.3.1	1.3.1
github.com/altcha-org/altcha-lib-go	go	< 1.0.0	1.0.0
org.altcha:altcha	maven	< 1.3.0	1.3.0
altcha	rubygems	< 1.0.0	1.0.0
altcha	pip	< 1.0.0	1.0.0
altcha	erlang	< 1.0.0	1.0.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability, identified as GHSA-6gvq-jcmp-8959, is a cryptographic semantic binding flaw across multiple ALTCHA libraries. The core issue lies in the createChallenge (or equivalent) function in each library. This function is responsible for generating a proof-of-work challenge. The salt parameter within this challenge was not being properly delimited. This allowed an attacker to perform 'challenge splicing' by appending their own parameters to the salt. Since the HMAC signature did not unambiguously bind the intended challenge parameters, an attacker could have a valid proof-of-work submission reinterpreted with a modified expiration value, enabling replay attacks.

The patches across all affected libraries (Go, Java, Ruby, JavaScript/TypeScript, PHP, and Elixir) address this by ensuring the salt string always ends with an ampersand (&). This acts as a delimiter, preventing an attacker from adding new parameters that would be misinterpreted by the server. The analysis of the provided commits confirms that the createChallenge function (and its equivalents) is the primary vulnerable function, as it is responsible for the insecure construction of the salt. In some libraries, the corresponding extractParams function was also updated to align with the new, correct salt format.

Vulnerable functions

org.altcha.altcha.Altcha.createChallenge

src/main/java/org/altcha/altcha/Altcha.java

The `createChallenge` function constructs the `salt` parameter used in the proof-of-work challenge. Before the patch, the salt was not properly delimited, allowing an attacker to splice additional parameters into the salt. This could be used to bypass the expiration check and replay a solved challenge. The patch adds a '&' delimiter to the salt to prevent this ambiguity.

createChallenge

altcha.go

The `CreateChallenge` function in Go constructs the `salt` parameter without a proper delimiter. This allows an attacker to perform parameter splicing, potentially leading to replay attacks by reinterpreting a valid proof-of-work with a modified expiration. The patch mitigates this by appending a '&' to the salt.

Altcha.create_challenge

lib/altcha.rb

The `create_challenge` method in the Ruby library is responsible for generating the challenge. The vulnerability lies in the construction of the `salt` where a missing delimiter allows for parameter splicing. The patch ensures a '&' is always appended to the salt, preventing attackers from manipulating the challenge parameters.

createChallenge

lib/index.ts

The `createChallenge` function in the TypeScript library was using a semicolon ';' as a delimiter for the salt, which is non-standard for URL parameters. This could lead to misinterpretation of the salt and its parameters. The patch changes the delimiter to an ampersand '&' for correct parsing.

extractParams

lib/index.ts

The `extractParams` function was modified to correctly parse the salt parameter after the delimiter was changed from a semicolon to an ampersand. The previous implementation was attempting to remove a trailing semicolon, which is no longer necessary with the correct delimiter.

BaseChallengeOptions::__construct

src/BaseChallengeOptions.php

The constructor of `BaseChallengeOptions` in the PHP library is responsible for preparing the salt. It was using a semicolon ';' as a delimiter, which is incorrect for URL parameters. This could lead to misinterpretation of the salt. The patch changes the delimiter to an ampersand '&'.

Altcha::extractParams

src/Altcha.php

The `extractParams` function in the PHP library was updated to handle the corrected salt format. It previously had to trim a trailing semicolon, which is no longer needed after the delimiter was changed to an ampersand in the challenge creation process.

Altcha.create_challenge

lib/altcha.ex

The `create_challenge` function in the Elixir library constructs the `salt` parameter. The lack of a delimiter allowed for parameter splicing. The fix adds a '&' delimiter to prevent ambiguity and potential replay attacks.

WAF Protection Rules

WAF Rule

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Reasoning

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6.5

-

Basic Information

Basic Information

Concerned about an active attack path?

CVE-2025-68113: ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay

Impact

Patches

Workarounds

CVE-2025-68113:

6.5

-

Basic Information

Basic Information

Technical Details

Technical Details

Vulnerability IntelligenceMiggo AI

Root Cause Analysis

Vulnerable functions

WAF Protection Rules

WAF Rule

Reasoning

Vulnerability IntelligenceMiggo AI

Technical Details

6.5

6.5

Basic Information

Basic Information

CVE-2025-68113: ALTCHA Proof-of-Work Vulnerable to Challenge Splicing and Replay

Impact

Patches

Workarounds

Vulnerability IntelligenceMiggo AI

Root Cause Analysis

Vulnerable functions

WAF Protection Rules

WAF Rule

Reasoning

Vulnerability Intelligence
Miggo AI

Vulnerability Intelligence
Miggo AI

Vulnerability Intelligence
Miggo AI